Reticles are provided in telescopes for sighting of a target, e.g. in a rifle telescope. A typical sighting or rifle telescope 2 is shown in FIGS. 1 and 2 of the drawings. Such telescope 2 typically comprises an optical system which is mounted in a tube 4 having different diameters.
At front portion 4a of the tube 4, which is usually of larger diameter, a front lens system 6 is provided. At an intermediate portion of the tube 4, which is typically referred to as center tube 4b, several adjustable optical elements are positioned. Furthermore, external turrets 8 including a turning knob 10 are positioned at the center tube 4b to adjust the optical properties of the optical system. An ocular or eyepiece 12 is provided at a back portion 4c of the tube 4, which is again typically of larger diameter than the center tube 4b. 
The optical system consists of at least the front lens system 6, an erector system 14, and a reticle 16. The optical system defines an optical axis A. The front lens system 6 can consist of a plurality of single lenses or cemented elements (so-called “Kittglieder”).
To focus an object 18 to be viewed through the sighting telescope 2 or for adaptation of an ametropie (refractive error) of the user's eye 20, the ocular 12 or a group of lenses being part of the front lens system 6, is axially movable. Such group of lenses may be positioned between the front lens and the erector system 14 and is sometimes referred to as focusing lens.
The front lens system 6 typically produces a real image, which is upside down relative to the viewed object, in a —with regard to the object—conjugated first focal plane F1. The axial position of the first focal plane F1 depends on the distance of the object 18 and can be influenced by the focusing lens.
The erector system 14 includes a fixed group of lenses or includes at least two axially movable zoom elements (14a, 14b) to erect the image. The upside down image is erected by the erector system 14 and is reproduced in another focal plane, namely the second focal plane F2 with a certain reproduction scale. Between the first and the second focal plane (F1, F2) further lens groups like a field lens 22 or Barlow lens may be positioned. All described optical elements may be provided with fittings.
An aperture and a reticle 16 can be provided near the first focal plane F1 conjugated to an infinitely distant object. Typically etched glass reticles or metal reticles are used.
If the erector system 14 includes at least two axially movable zoom elements (14a, 14b), those provide a double function, namely to erect and reproduce the image of the first focal plane F1 in the second focal plane F2 and to allow continuously adjusting the magnification of the image perceived by the user within a mechanically limited range. The reproduction scale of the erector system 14 varies continuously between the first and the second focal plane conjugated to the first focal plane F1.
An aperture and the reticle 16 may also be provided near the second focal plane F2, again typically an etched glass reticle or a metal reticle.
The reticle 16 defines a sighting line which is brought in line with the target object 18. The user can shift the sighting line with the turrets 8 to adjust the point of impact. E.g. ballistic drop of the projectile or lateral offset caused by wind can be compensated. Furthermore, the user can use the focusing lens to obtain a parallax-free image (i.e. the sighting point does not move relative to the object, when the user's eye 20 laterally moves) which is as sharply focused as the reticle 16 independently of the distance of the object 18 even when using a sighting telescope 2 having a large magnification scale.
A zoom position typically means a user-defined magnification adjustment within the mechanically possible adjustment interval of the magnification range of the sighting telescope 2.
A zoom factor is the ratio of two magnifications wherein the larger magnification is put in the numerator. A maximum zoom factor is the ratio of the mechanically possible maximum and minimum magnification of the sighting telescope 2 wherein the larger magnification is put in a numerator.
The ocular 12 is used to reproduce the image of the second focal plane F2 in an arbitrary distance, e.g. at infinite distance or in a virtual distance of one meter, or to focus on the reticle 16.
A ray direction can be defined by the order: object 18, front lens system 6, erector system 14, ocular 12, eye 20.
The fittings of the optical elements or the aperture near the second focal plane F2 limit the subjectively perceived visual field, depending on the adjusted magnification.
If the user zooms from the mechanically maximum possible magnification to the mechanically minimum possible magnification this can change the limitation of the visual field from the aperture near the second focal plane F2 to a fitting of another optical element in front of the second focal plane F2, thereby reducing the visual field. This effect is called “tunneling effect”.
The aperture can be defined either by a separate aperture stop or by the fitting of an optical element, which may be different fittings depending on the adjustment of the magnification. The aperture can be reproduced in a plane which is downstream of the ocular—typically at a distance of 70 mm to 100 mm to the ocular—by the remaining optical system. This plane is called “plane of the exit pupil”.
The portion downstream of the ocular 12 in which the eye 20 of the user is positioned to view the whole visual field is called “eye box”.
An ametropie of the user's eye 20 can be adjusted by a diopter compensation. For this, the axial position of the ocular 12 can be adjusted.
The sighting telescope 2 may comprise further optical components e.g. an illumination of the reticle, a coupling system for coupling in or out of light rays, e.g. for distance measurement or photography. Furthermore, electronic components, sensors, actuators or batteries may be included.
Typically glass reticles are wet etched which is a complex production process requiring many working steps and high manpower. Furthermore, such production process needs substantial infrastructure and space requirements and is harmful to the environment because of the chemistry used. Furthermore, such production process is inflexible because of the lithographic process used. A lithographic process typically includes producing of a mask original, replications of the original etc., so that it takes typically six weeks from design to the production of the first piece. The high fix costs of such process are further disadvantageous, so that it is hard to react when production numbers shift between different reticles.
If a wet etched glass reticle shall be illuminated, the etched structures are typically filled with a light scattering filling material like a titanium oxide containing lacquer or the like.
However, these production processes for illuminated glass reticles are cumbersome and expensive. Furthermore, the brightness and precision of an etched and titanium oxide filled structure to be illuminated may be subject to further improvement.